The present invention relates generally to the art of manufacturing ribbon cartridges for printers used with computers and word processors, and, more particularly, to a method and apparatus for loading the ribbon into the cartridge.
Various types of printers are used with computers and word processors. One common type is an impact printer where each character is permanently embossed on a striking surface and the printing of a particular character is accomplished by striking the character against a printer ribbon disposed adjacent the paper surface onto which the characters are to be printed. Another type of printer is the dot matrix printer. The dot matrix printer uses wires arranged in a two-dimensional matrix such that each wire may be independently extended to contact a printer ribbon to print a dot image on the adjacent paper surface. By selectively extending particular patterns of wires, dot images can be combined to form characters on the paper surface. The printer ribbon has ink thereon so as to result in an ink image of the character on the surface of the paper. Printer ribbons typically are made of fabric, such as nylon, or polyester film coated with a carbon-type surface.
In approximately 1970, continuous loop printer ribbon cartridges began appearing on the market. Printer ribbon cartridges include a plastic housing made up of a base shell and a cover shell. Within the cartridge there may be mounted an internal drive mechanism to move the ribbon through the cartridge envelope. The drive mechanism is mounted at one end of the cartridge envelope and often a tension clip is mounted on the other end of the cartridge envelope to maintain tension on the ribbon. The cartridge is loaded with a length of nylon or other fabric ribbon housed in serpentine fashion within the cartridge envelope and the two ends of the printer ribbon are adjoined to form a continuous loop. These continuous loop printer ribbon cartridges are easily removed from and inserted within the printers. Such continuous loop cartridges mechanically simplify the ribbon control portion of printers and thereby eliminate a potential source of failure.
Efforts are continually being made to automate the manufacture of ribbon cartridges. Originally, ribbon cartridges were manually assembled. In the assembly of the cartridge, a drive mechanism is mounted within the base shell. A length of leader ribbon is threaded through the apertures in the envelope of the housing. The ends of the leader ribbon are left extending outside the cartridge. After the leader ribbon is in place, the cover shell of the cartridge is press fitted onto the base shell to enclose the cartridge housing. The exposed ends of the leader ribbon are then attached to the end of an inked printer ribbon. The leader ribbon is then used by the cartridge drive members or an external drive member to draw the appropriate length of inked printer ribbon into the envelope of the previously assembled cartridge. As the motor rotates the drive mechanism, the inked ribbon is folded in a serpentine fashion within the cartridge envelope. Upon completion of the loading, the ribbon is de-leadered and the two free ends of the inked ribbon are welded into a continuous loop by a welder. One apparatus particularly useful in automatically stuffing the assembled cartridge with inked printer ribbon is described in U.S. Pat. No. 4,609,422.
In manufacturing printer ribbon cartridges, it is necessary that the proper length of leader ribbon be used upon assembly of the cartridges. If the leader ribbon does not have the proper length, the ribbon loading apparatus will not be able to load the cartridge with inked ribbon. If the leader is too short, the ribbon loading apparatus will not be able to fully load the cartridge and, if the leader ribbon is too long, the operator must manually jog the drive motor of the ribbon loading apparatus to take up the excess leader. Improper leader length results in waste and additional labor costs.
The automated ribbon manufacturing system practiced by the applicant includes a series of operations stations connected by a transport conveyor with the operations stations and transport conveyor being microprocessor operated and controlled. To convey a ribbon cartridge from station to station, individual cartridges are mounted on nest plates disposed on pallets that are conveyed between the stations by the transport conveyor. The operations stations include the pallet leadering station, the preliminary cartridge assembly station, the completed cartridge assembly station, the cartridge cover press station, the cartridge loading station, and the welding and winding station.
Initially, an empty pallet with a nest plate for a particular size and shape cartridge is positioned at the pallet leadering station where the accumulator on the pallet is filled with a pre-selected length of leader. A robotic arm carries the end of the leader and threads it into the accumulator. The accumulator drive rollers then fill the accumulator with a pre-selected length of leader and the end of the leader is cut. The pallet then moves to the preliminary cartridge assembly station. At that station, the base shell of the cartridge is manually inserted into the nest on the pallet. The drive elements for the cartridge are installed in the cartridge base. The pallet and cartridge base are then moved to the completed cartridge assembly station. There, the end of the leader extending from the accumulator on the pallet is manually threaded through the drive elements and cartridge envelope with the ends of the leader clamped by clamping assemblies located at the corners of the pallet. Any remaining parts of the cartridge are also installed. The cover of the cartridge is then placed over the base. The transport conveyor then moves the pallet to the cartridge cover press station. There, the cover is pressed onto the base.
After the cartridge is assembled, the pallet moves onto the main transit line where a microprocessor properly routes the cartridge for cartridge loading, de-leadering, welding, and winding. At the cartridge loading station, a gripper arm grasps that end of the leader extending from the drive element end of the cartridge and threads the leader end to the tack welder where that end of the leader is clamped. The welder tack welds the ends of the leader to the free end of a length of inked ribbon mounted on a master spool. The other end of the leader extending from the cartridge is pulled by a gripper assembly arm into a set of drive and driven rollers which pull the leader from the cartridge until the inked ribbon is pulled completely through the cartridge envelope. As the leader is pulled through the set of drive and driven rollers, it is sucked away by a vortex and cut off when the operations station senses the inked ribbon. The end of the ribbon is then clamped onto the pallet. The inked ribbon must be loaded into the cartridge envelope simultaneously with the pulling of the leader so as to provide a supply of inked ribbon to replace the leader within the cartridge envelope as the leader ribbon is removed. Simultaneously with the gripper arm assembly pulling the leader and inked ribbon through the cartridge envelope, the drive elements on the cartridge are activated by a motor drive so as to commence the loading cycle during the time the leader is being removed. The ribbon is folded in a serpentine manner within the cartridge envelope. The ribbon is cut from the master spool. The ends of the ribbon are now clamped by the clamping assemblies on the pallet. The pallet then moves to the welding and winding station where the ends of the ribbon are tensioned for the welding operation. The ends of the ribbon are welded and cut discarding the trim. The welded ribbon is ironed and the ribbon is wound into the cartridge to take up the slack left from welding. The cartridge is then ready to be sent to packaging.
The automation of the manufacture of printer ribbon cartridges is severely hindered by the large number of different printer cartridges. There is estimated to be over 500 different sizes and configurations of printer ribbon cartridges severely restricting the ability of the manufacturer to design uniform automation equipment that can handle this wide variety of cartridge designs during each of the individual manufacturing operations. Thus, continuous efforts are being made on improvements in the manufacturing process and apparatus to universally accommodate these multiple cartridge designs in the automated manufacturing process.
In particular, because there are such a variety of cartridge sizes and shapes, it is very difficult to configure the apparatus and process for loading this large variety of cartridge sizes and shapes with inked ribbon. With such a wide variety of cartridge designs, a different nest plate must be used for each of the different cartridges throughout the process so as to accommodate the loading, welding and winding operations. The ideal manufacturing operation would be able to accommodate all sizes and configurations of cartridge and all types and widths of printer ribbons without requiring different nest plates or substantial changes in the setup of the individual manufacturing operations.
The prior art system of loading a printer ribbon cartridge with inked ribbon included using the cartridge drive mechanism to draw the inked printer ribbon into the envelope of the cartridge. The drive mechanism of the cartridge comprises drive and driven rollers are made of thermoplastic. The thermoplastic will deteriorate if rotated at high speeds. For example, a thermoplastic cartridge drive made of Delrin manufactured by E. I. DuPont Corporation will operate at speeds up to 3900 rpms without lubrication. However, thermoplastic cartridge drives made of other plastics such as styrene will only operate at speeds up to 2000 rpms. The drive mechanism of a printer cartridge is never operated above 1000 rpms during normal printing operation and therefore the mechanism is not designed to operate at high speed rotation. The torque applied to the thermoplastic journals on the cartridges during the ribbon loading operation requires that the cartridge drive mechanisms be operated at limited speeds due to the limited capability of the mechanism. It is preferred that the cartridge loading operation be performed at high speeds not only to save machine time but also it has been found that high speed loading causes the serpentine folds to be more evenly spaced and distributed within the envelope of the cartridge. To overcome the deficiencies of using the thermoplastic cartridge drive mechanism for the ribbon loading operation, it is preferred to use external drives having precision journal bearings that will allow high speed rotation to not only reduce ribbon loading time but also to allow more even serpentine folds within the cartridge envelope.